How to set up a used hot tub: a step-by-step guide

The hot tub has arrived, it is standing in the garden, and you would love to get in this evening. With a used hot tub, though, the first day matters more than with a new one: you do not know exactly how it spent the winter, how it coped with transport and what was left in the pipes. This guide walks through the setup in the order an experienced technician would follow, from the base to the first soak. It takes few tools and a fair amount of patience: a calm, careful first day lays the foundation for years of trouble-free use.

In what order should you set up a used hot tub?

The right order is: base and level, electrical connection, inspection behind the cabinet, cleaning, filling through the filter housing, bleeding the air, first start-up and heating, and finally balancing the water. There is a reason for this order: only a full hot tub may get power, chemicals only go into circulating, clear water, and you should only bathe in balanced, sanitized water.

1. Checking the base and the level
2. Electrical connection by a qualified electrician
3. Inspection after transport, with the cabinet panels removed
4. Cleaning the shell before filling
5. Filling through the filter housing
6. Preventing and clearing air locks
7. First start-up and heating
8. Balancing the water: alkalinity, pH, sanitizer

What should you look for in the base and the level?

The hot tub needs a flat, level, load-bearing surface that supports it evenly and will not sink later. Filled and with bathers in it, a family hot tub weighs several tonnes, and if that weight is not evenly distributed, the shell and the frame will suffer over time.

• Level. Place a long spirit level on the rim of the hot tub lengthwise, crosswise and diagonally. Even a small deviation will show in the water line and put stress on the structure.
• Do not shim. Only level the hot tub with shims or wedges if the manufacturer explicitly allows it. On some models it is expressly forbidden, because it creates point loads. The right solution is a level base.
• Material. Outdoors, manufacturers typically recommend a reinforced concrete slab. For a deck or a roof terrace, get a structural engineer's opinion.
• Access. The pumps, heater and controls sit behind the cabinet panels. Leave enough room on the service side to remove the panel and for a technician to work comfortably.
• Drainage. Water should not pool around the hot tub: rain, splashes or a possible leak must all be able to drain away.

Who should connect the hot tub, and how?

The hot tub must always be connected by a qualified electrician, per local regulations, on a dedicated circuit with a residual current device (RCD). This is no formality: water and electricity meet here, and the quality of the connection directly affects the safety of the people in the water.

• The requirements are on the rating plate. The required voltage, the type of supply (single-phase or three-phase) and the current draw are given on the hot tub's rating plate and in the manual. The same model can be configured differently by country and year, so the electrician should go by that, not by a generic table.
• Residual current device. Manufacturers' instructions typically specify an RCD with a tripping current of a maximum of 30 mA. Many manufacturers also ask for an easily accessible isolating switch near the hot tub, so the power can be safely cut for servicing.
• Never an extension lead. Running a hot tub from a cable reel or an extension lead is not allowed, not even "just for a few days".
• With a used hot tub, pay extra attention to whether a cable gland or a cover is missing from the connection box after the previous installation, and whether the supply cable was damaged in transport.

What should you check after transport, before filling?

Remove the service panel (or the cabinet panels) and look at the pipe connections, the pumps and the heater before a single drop of water goes in. Vibration during transport can loosen the union nut connections; manufacturers warn about this too, and it can usually be fixed by hand.

• Union nuts. The large plastic threaded connections on both sides of the pumps and the heater should be hand-tight. If the seller loosened them when draining (common for winterising), tighten them now. Do not force them with pliers, as the plastic thread can be damaged.
• Gate valves. If there are gate valves before and after the pumps, check that they are open. With a closed gate valve the pump runs dry.
• Drain valve. It should be closed, with its cap in place.
• Cracks. Look over the pipes, the pump housing and the heater. A hairline crack, white efflorescence, an old scale streak or a rust stain all point to an earlier leak.
• Insulation and cables. Rodent traces, waterlogged foam insulation, a damaged cable: all signs that are better spotted now than after filling.

If the hot tub stood or was transported in winter

If a hot tub froze with water in its pipes, the ice can split the pump housing, the heater tube, the plastic pipes and fittings. Frost damage is often invisible when dry: it only shows once the system is under pressure. So with a hot tub transported in winter or poorly winterised, the first minutes of filling matter most: fill slowly and keep an eye on the area behind the cabinet.

What should you clean the shell with before filling?

Clean the shell with a soft cloth and a shell cleaner made specifically for hot tubs (or the product named in the manual), never with household cleaners. According to manufacturers, most household chemicals, alcohol, abrasive and solvent-based products can damage the acrylic surface, and their residues later cause foaming in the water.

• Sweep out leaves, dust and transport dirt, including from the filter housing.
• After cleaning, rinse the surface thoroughly with clean water, and drain or wipe up the rinse water.
• Look at the jets: on a used hot tub they often contain deposits. The faces of many jets can be unscrewed and cleaned.

Cleaning the plumbing

Biofilm (a slimy deposit) from previous years' water can remain in the pipes of a used hot tub, and it quickly spoils fresh water. It can be flushed out with a line flush liquid, which you add to the old water before draining and circulate with the pumps running. If the hot tub arrived empty, the first fill can serve as a cleaning fill: you fill it, flush it, drain it, and only then comes the final water. We describe the details in a separate guide.

How should you fill the hot tub?

Fill the hot tub with a garden hose through the filter housing: put the hose where the removed filter cartridge sits, into the filter standpipe. That way the water flows in through the pumps and the heater and pushes the air out of the pipes ahead of it. If you just put the hose into the hot tub, there is a greater chance that an air lock remains in the system.

• Open the jets. The adjustable jets should be open so the air can escape from the pipes.
• A pre-filter on the hose. If your water is hard, contains iron or comes from a borehole, use a hose-end pre-filter or a metal-removing cartridge. These filter out iron, copper, manganese and dirt that could otherwise stain the shell and make water care harder. With a new carbon filter cartridge, let the first few litres run to waste until the water runs clear, as the product instructions say.
• Not with softened water only. Most manufacturers do not recommend filling the hot tub exclusively with water from a water softener, because water that is too soft can be corrosive to metal parts and prone to foaming. With very hard water, a common solution is to fill with half hard, half softened water. Your manual gives the exact recommendation.
• Not with hot water. Do not fill from the household hot water system. Some manufacturers (for example Hot Spring and Caldera) also advise against very cold fill water below 10 °C, because it can trip the overheat protection. In winter, check what your manual says about this.
• Not with pool water. Do not transfer water from a swimming pool: its chemical treatment is completely different.
• Water level. Fill until the water is above the highest jets but below the headrests. In many hot tubs a mark on the wall of the filter housing shows the correct level.

While filling, check behind the cabinet several times. If you see a drip at a connection, hand-tightening the union nut is usually enough. If the water is coming from a crack, however, stop filling.

How do you avoid an air lock, and what should you do if one forms?

An air lock is air trapped in the pipes or the pump: the pump hums, but no water comes out of the jets, or only a weak, pulsing stream. The best prevention is filling through the filter housing, but with a drained, transported hot tub it can still happen.

What should you do if the pump hums but nothing flows?

1. Switch it off quickly. The pump must not run dry: manufacturers give an upper limit of a few minutes (some say two minutes), after which the seal and the motor can be damaged.
2. Use the priming mode. Many control systems (for example Balboa and Gecko) enter a priming mode for a few minutes at start-up, shown as "Pr" on the display. During this time you can help the air escape by switching the pumps on and off one at a time, briefly.
3. Loosen the union nut. If that does not help either: cut the power at the circuit breaker, remove the panel and slightly loosen the union nut on the pressure side of the pump (typically on top of the pump). The air hisses out, then water appears. Then hand-tighten it again.
4. Switch back on and check. Restore the power, start the pump and check that the tightened connection does not leak.

If your hot tub has an air bleed valve at the filter housing, you can also let the air out with that. Some manufacturers also suggest briefly pushing water into the system by fitting the hose onto the suction fitting where the filter was removed (with a rag wrapped around it). Always follow the method in your manual.

What happens at first start-up and during heating?

After filling, switch the hot tub on at the circuit breaker, check that every pump runs with a strong, even stream, then set the desired temperature and put the cover on. The first heat-up is a long process, and that is completely normal.

• Testing the pumps. Switch the pumps on one at a time, on high speed as well. If the jets blow strongly without pulsing, the system is free of air.
• Leaks under pressure. With the pumps running, look behind the cabinet again. What was dry with still water may start dripping under pressure.
• Temperature. The factory default is typically around 38 °C, and the upper limit on most hot tubs is 40 °C. Setting a higher temperature does not make it heat faster, it just ends up warmer.
• Heat-up time. Depending on the volume of water, the fill water temperature, the heater output and the weather, it takes several hours, often up to a full day. Some manufacturers allow 18-24 hours to reach 38 °C.
• Cover on throughout. While heating, keep the cover on the hot tub, secured with its locks. Without the cover, most of the heat escapes.

In what order should you balance the water?

Balance fresh water in this order: first the alkalinity (TA), then the pH, and finally the sanitizer. Alkalinity acts as a buffer that holds the pH steady, so until it is right the pH jumps around, and sanitizer does not work effectively at the wrong pH.

1. Alkalinity (TA). Test it and raise or lower it if needed.
2. pH. Once the alkalinity is right, adjust the pH.
3. Sanitizer. Only then add chlorine or bromine (or the sanitizer for your chosen system), and check that the level stays stable.

Manufacturers' manuals typically give these ranges:

In this range, mg/l and the ppm often shown on test strips mean practically the same thing. Water hardness (calcium content) is also part of the balance; manufacturers give different values for it, so here your own manual is especially the reference. If the hot tub has a UV-C, ozone or salt system, the target values may differ.

How should you dose?

• Add chemicals in front of or into the filter housing with the pump running, and let them circulate for at least ten minutes.
• Work in small doses: dose, circulate, wait, test again. With a large amount at once it is easy to overshoot the target.
• After shocking, leave the cover open for at least 20 minutes so the gases can escape. Vapours trapped under the cover damage its inner lining and foam.
• Manufacturers do not recommend chlorine tablets (trichlor) for hot tubs, because they corrode components. Use products made specifically for hot tubs.

Test strips or a drop test?

Test strips are quick and convenient, good for everyday checks. A drop test (liquid or tablet reagent) is more accurate, because instead of judging a shade of colour you count drops until a clear colour change. For the first balancing, and whenever a strip shows an odd reading, it is worth testing with a drop test too. Keep test strips closed, in a dry, cool place, because humidity quickly ruins them.

The hot tub is ready to use when the water is at a comfortable temperature and the sanitizer level is still within the recommended range after a few hours.

What should you watch in the first week?

In the first week, test the water daily and keep an eye on how the hot tub runs: this is when you find out whether everything is stable. After that you can test less often, as the manual says, but at least weekly and after heavier use.

• Water values. Fresh water still shifts in the first days. Follow how the alkalinity, pH and sanitizer change, and correct little by little.
• Foaming. If the water foams, it often points to cleaner residue or old deposits being released from the pipes. With heavy foaming, a line flush and a refill may be the solution.
• Behind the cabinet. After a few days, look behind the panel again. A slow drip only leaves visible traces over several days.
• Filtration cycles. Check which filtration programme the control system is set to, and adjust it to your use as the manual describes.
• Heat retention. If the water cools noticeably overnight, or the heater runs almost constantly, the cover or the insulation may be the weak point.

Should you fit a new filter, or is cleaning the old one enough?

With a used hot tub it is best to start with a new filter cartridge, because you do not know how long and what kind of water has passed through the old one. If the old cartridge is intact (the pleats are not torn or loose and the end caps are not cracked), it can be used temporarily after a thorough clean, but it is worth getting a spare.

• Soak the old cartridge in filter cleaning solution, then rinse thoroughly between the pleats with a hose. Cleaner residue causes foaming, so do not skimp on rinsing.
• Before fitting it, submerge the cartridge in the water and tilt it until the bubbles stop. Air trapped in the cartridge can also cause an air lock.
• Never run the hot tub without a filter cartridge.

If you want to make water care simpler, there are product ranges designed to work together for filter cleaning and water care (AquaFinesse is one example), but any quality product made for hot tubs will do if you use it as the manual describes.

What should you check on the cover?

Check that the cover is not heavy, that it seals well and that its locks work. The cover keeps the heat in and also protects children, so it is part of the setup.

• Weight. If it is unusually heavy, the foam core has soaked up water, insulates poorly and needs replacing.
• Fit. It should sit on the rim all the way round, with no gap at the fold where steam can escape.
• Seams and hinge. Behind a torn cover at the fold, the foam soon becomes waterlogged.
• Locks. The straps and locks should be intact, and use them whenever nobody is at the hot tub.

Do not stand or sit on the cover, and do not treat it with silicone or solvent-based products, because they dry out the vinyl.

When should you call a technician?

Call a professional if the display shows an error code that comes back after a restart, if the residual current device trips, or if you see a leak that does not stop after hand-tightening. These are not worth experimenting with.

• The RCD trips. This can point to an earth fault or an insulation fault. Do not keep switching it back on: call an electrician or a hot tub technician.
• Error codes. Flow, sensor and overheating errors (codes vary by control system, for example FL, SN, OH, HL) can have a simple cause (a dirty filter, low water level, an air lock), but if they come back after you have dealt with those, you need a technician.
• Leaks. A cracked pipe, pump housing or heater tube, or a pump that keeps dripping at the seal: that is a repair, not a matter of tightening.
• No heating. If the water has not warmed up noticeably after a day, even though the cover is on and the settings are right.
• Noisy pump. Squealing, loud humming or a pump that cuts out from overheating can point to a worn bearing on an older hot tub.